1. Field of the Invention
This invention is concerned with surfactant waterflooding in subterranean reservoirs.
2. Description of the Prior Art
In copending application Ser. No. 259,216, filed Apr. 30, 1981, there is disclosed a class of homologous sodium branched alkylpolyethyleneoxy propane sulfonates. The compounds differ from each other primarily in the size of the hydrophobe, i.e., the number of carbon atoms in the branched alkyl group. Each compound has a range of salinities in which it is effective, i.e., salinity window.
In formations having extremely low porosity, however, ultra low interfacial tensions are necessary, below about 10 millidynes (0.01 dyne) per centimeter. With this requirement, the effective salinity range of each surfactant described in Ser. No. 259,216 is relatively narrow. In order to provide ultra low interfacial tension for fields having salinities throughout the range of about 4-30% salinity, a plurality of surfactants would have to be available. It is the discovery of this invention that, by blending two or more homologs, a desired salinity window can be obtained with a small number of surfactants. Insofar as is now known, this has not been proposed.